The ADA stuff on the web is a big deal. Any graphic arts/web programming school teaches it. There are special readers that read alt tags, and all the text on a web page. It is a slow process, especially compared to how quickly sighted people can go through the web. The readers work well although sometimes can pick up some tags.
It just means a little more effort has to go into site creation, but I think over all it is not that big of a deal to throw in a few tags here and there to make it possible for people with disabilities to use a site.